Embodiments of the invention relate to bearings, in particular magnetic bearings used in rotary machines having a rotor.
In particular, the embodiments of the invention relate to active magnetic bearings having electromagnetic elements arranged in the radial direction and adapted to cooperate with a rotor circuit secured to the rotor.
Axial magnetic bearings use electromagnetic forces pulling in opposition on the thrust collar secured to the rotor shaft to maintain relative position of a rotating assembly (rotor) to a stationary component (stator). A thrust collar is generally a flat, solid, ferromagnetic disc secured to the rotor. Disc-shaped electromagnetic elements are located on either side of the thrust collar and bolted to the rotary machine housing, forming the active axial magnetic bearing.
Use of magnetic bearings in rotary machines is becoming more and more widespread, in particular in case of corrosive or hot fluid. The inner ventilation of the magnetic bearing is thus important to increase the service-life of the bearing.
The friction generated by the relative movement of the thrust collar with respect to the electromagnetic elements creates a radial flow of fluid which leads to the cooling of the magnetic bearing.
However, such flow is dependent of the friction between two components and the rotational speed of the rotor, and is thus not reliable. Furthermore, because of uncertainty in the pressure distribution, a back flow could appear which would lead to a lack of flow of cooling fluid.
Current magnetic bearings do not provide enough inner ventilation, so that the flow of fluid becomes insufficient to cool the axial magnetic bearing.